EP2942673A1 - Mechanical oscillator with tuning fork for clock movement - Google Patents

Abstract

Wristwatch comprising a mechanical watch movement with a resonator of the tuning fork type. The oscillator preferably comprises a material A with low internal friction. In the oscillator of the invention, the undesired symmetrical oscillations are avoided, for example, by the choice of materials whose tuning fork is manufactured. According to preferred embodiments, the rod and / or the fixation of the oscillator comprises a material having a greater internal friction than that of said material A, so that the quality factor Q ₂ of the symmetrical oscillations is decreased, contrary to the quality factor Q ₁ of the antisymmetric oscillation mode.

Description

Technical area

The present invention relates to an oscillator of the tuning fork type, a watch movement comprising the oscillator and a timepiece comprising the oscillator. In particular, the invention relates to a mechanical timepiece comprising the oscillator.

State of the art and problems at the origin of the invention

An object of the present invention is to improve the performance of the mechanical movement of a timepiece, in particular a mechanical timepiece. The sprung balance, long used as an oscillator in mechanical watches, has proven itself, but despite, or perhaps because of, centuries of research and development, it may be close to its limits . Thus, the best balance springs achieve a quality factor Q of about 300. The quality factor of an oscillator being defined by the formula Q = 2π x (stored energy / energy lost in each period), it essentially represents the number of oscillations after which the oscillator loses all its energy and stops.

The tuning fork is well known for its basic qualities of time, the tuning-fork wristwatches of the 1960s were the most accurate in the world until the advent of the quartz watch. Max Hetzel is at the origin of a large number of patented inventions, relating to the implementation of a tuning fork as an oscillator, which led to the production of the Accutron wristwatch (registered trademark), marketed by the Bulova Swiss SA company.

The Accutron watch, however, includes an electronic resonator as each branch of the tuning fork carries a permanent magnet associated with an electromagnet mounted fixed on the frame of the watch. The operation of each electromagnet is slaved to the vibrations of the tuning fork by means of the magnets it carries, so that the vibrations of the tuning fork are maintained by the transmission of periodic magnetic pulses from the electromagnets to the permanent magnets. One of the branches of the tuning fork actuates a pawl for rotating the mobile wheels of the finishing gear of the watch.

The patent US 2,971,323 for example, from a deposit dating back to 1957, describes such a mechanism that can not however be suitable for the realization of a purely mechanical watch, that is to say without electronic circuits. Indeed, a real need exists, in terms of market, for purely mechanical timepieces with increased running accuracy compared to known parts.

A general difference between mechanical wristwatches and acoustic tuning electronic watches is the fact that, in the latter, the oscillator as a time regulator also serves as a power distributor, that is to say that the oscillations are used to actuate the movement (Accutron) or to determine the activity of an electric motor which acts on the needles, for example (quartz electronic watch). On the other hand, in mechanical watches, regulation is at the end of the chain of energy transmission.

The patent US 3,208,287 , from a deposit dating from 1962, describes a resonator comprising a tuning fork coupled to an escape wheel by means of magnetic interactions. More specifically, the tuning fork carries permanent magnets cooperating with the escape wheel, the latter being made of a magnetic conductive material. The escape wheel is kinematically connected to a source of energy which may be mechanical or take the form of a motor, while it comprises openings in its thickness such that it forms a magnetic circuit of variable reluctance when it is driven in rotation, in relation with the magnets carried by the tuning fork. This patent mentions an "abnormal oscillation", illustrated in FIG. 9. It is indeed a symmetrical oscillation which, according to this patent, can be avoided by positioning the escape wheel so as to act, in same time, on both blades of the oscillator, as shown in figures 2 and 3 . This solution resembles that used in electronic quartz watches (as well as the Accutron watch mentioned above) in that the symmetrical oscillation mode is imposed by the simultaneous pulse to both blades.

Compared to the patent US 3,208,287 the present invention seeks to solve several technical problems. On the one hand, it is desired to induce an antisymmetric oscillation by acting on a single blade of the tuning fork, therefore without imposing the antisymmetric oscillation by the simultaneous pulse of the two blades. On the other hand, the use of magnets to distribute energy to an oscillator (exhaust pulse) or to regulate an energy is not strictly speaking "mechanical", for the simple reason that the energy is transmitted by magnetic forces and therefore associated with electromagnetic phenomena.

This same reasoning is valid for the teaching of the European patent application EP 2 466 401 .

In view of the foregoing, the present invention aims to provide a mechanical movement watch having a more accurate time base than that of the conventional sprung balance. It is an object of the present invention to provide an oscillator characterized by a higher quality factor than that of the sprung balance.

In particular, an object of the invention is to provide a fully mechanical movement wristwatch using a tuning fork oscillator as a timebase.

An object of the present invention is to avoid, in a tuning fork oscillator, the symmetrical oscillations. More particularly, the present invention aims to avoid symmetrical oscillations in an oscillator comprising a material characterized by a low internal friction, so as to make the oscillator capable of performing said symmetrical oscillations.

An object of the invention is to provide a tuning fork on the basis of a material having a low internal friction such as monocrystalline silicon. The use of such a material makes it possible to increase the quality factor Q of the oscillations, but makes the tuning fork capable of carrying out undesired symmetrical oscillations in the context of a time base.

An object of the present invention is to provide an oscillator in which the antisymmetric oscillations are favored, even if the pulses are given on only one of the two blades, in other words, in the absence of simultaneous pulses. with both blades.

The present invention seeks to solve the above problems and has other advantages which will become more apparent upon reading the description and the claims.

Summary of the Invention

In one aspect, the present invention relates to a timepiece comprising a mechanical watch movement comprising: a tuning fork type oscillator, said oscillator comprising an assembly comprising two blades and a base connecting said blades, said oscillator comprising a rod connected to said base the oscillator being connected by its rod to a fastener connected to the movement, said assembly comprising or consisting of a material A, said material A being characterized by a weak internal friction, said movement comprising a mechanical pulse member capable of acting on one of the two blades so as to induce and maintain said oscillation oscillator, said oscillator being capable of oscillating in a desired antisymmetric mode as well as in an undesired symmetrical mode, characterized in that the factor quality Q ₂ symmetrical oscillation mode of said oscillator is reduced compared to the factor of Q ₁ quality of the antisymmetric oscillation mode.

In one aspect, the present invention relates to an oscillator of the tuning fork type, said oscillator comprising an assembly comprising two blades and a base connecting said blades, said oscillator comprising a rod connected to said base, the oscillator being connected by its rod to an organ fastener connected to a support, said assembly being formed of a material A, characterized by a weak internal friction, said oscillator being able to oscillate in a desired antisymmetric mode as well as in an undesired symmetrical mode, characterized in that the quality factor Q ₂ of the symmetrical oscillation mode of said oscillator is reduced with respect to the quality factor Q ₁ of the antisymmetric oscillation mode.

In one aspect, the present invention relates to an oscillator of the tuning fork type, said oscillator comprising two blades and a base connecting said blades, said oscillator comprising a rod connected to said base, characterized in that, in said oscillator, an oscillation mode symmetrical is damped or prevented by the presence of a selected material in or on said oscillator and / or in or on an attachment of the oscillator.

In one aspect, the present invention relates to an oscillator of the tuning fork type, said oscillator comprising two blades and a base connecting said blades, said oscillator comprising a rod connected to said base, the oscillator being connected by its rod to an attachment, said oscillator being made of one or more materials making said oscillator capable of performing symmetrical oscillations, and said oscillator or fixture further comprising another material capable of damping said symmetrical oscillations.

In one aspect, the present invention relates to an oscillator of the tuning fork type, said oscillator comprising two blades and a base connecting said blades, said oscillator comprising a rod connected to said base, the oscillator being connected by its rod to a fixation, said oscillator comprising or being made of several materials including a material A and a material A ', the material A' being characterized by a coefficient of thermal expansion of opposite sign to that of the material A.

In one aspect, the present invention relates to a movement for a timepiece comprising the oscillator and a timepiece comprising the oscillator.

In one aspect, the present invention relates to the use of a material having a comparatively high internal friction to avoid symmetrical oscillation in a tuning fork type oscillator.

Description of the drawings

• La figure 1 représente une vue schématique d'un diapason horloger.
• Les figures 2 A et 2 B illustrent l'oscillation antisymétrique et symétrique, respectivement, d'un diapason.
• La figure 3 A représente une vue schématique d'un diapason selon un premier mode de réalisation de l'invention.
• Les figures 3 B et 3 C représentent des vue schématiques des oscillations antisymétriques et symétriques, respectivement, de l'oscillateur de la figure 3A.
• La figure 4 A représente une vue schématique d'un diapason selon un deuxième mode de réalisation de l'invention.
• Les figures 4 B et 4 C représentent des vue schématiques des oscillations antisymétriques et symétriques, respectivement, de l'oscillateur de la figure 4A.

The features and advantages of the invention will emerge more clearly on reading a description of a preferred embodiment, given solely by way of example, in no way limiting with reference to the schematic figures in which:

• The figure 1 represents a schematic view of a watch tuning fork.
• The figures 2 A and B illustrate the antisymmetric and symmetrical oscillation, respectively, of a tuning fork.
• The figure 3 A represents a schematic view of a tuning fork according to a first embodiment of the invention.
• The figures 3 B and 3 C represent schematic views of the antisymmetric and symmetrical oscillations, respectively, of the oscillator of the figure 3A .
• The figure 4 A represents a schematic view of a tuning fork according to a second embodiment of the invention.
• The figures 4 B and 4 C represent schematic views of the antisymmetric and symmetrical oscillations, respectively, of the oscillator of the Figure 4A .

Detailed description of preferred embodiments

The present invention relates to an oscillator of the tuning fork type as well as a timepiece comprising the oscillator and still a movement for a timepiece comprising the oscillator.

The timepiece according to the invention may be a watch, a pocket watch, a pendant watch, a clock, or a table clock, for example. According to a preferred embodiment, the timepiece according to the invention is a wristwatch.

The timepiece according to the invention may be entirely mechanical and / or may comprise a fully mechanical movement. Preferably, an entirely mechanical movement can operate in the absence of any electronic circuit, in particular in the absence of a source of electrical energy, such as a battery or a photovoltaic cell, for example. The present invention also makes it possible to produce a timepiece that operates on the basis of mechanical interactions between all the parts and excludes magnetic interactions. In a fully mechanical movement, the pulses for inducing and maintaining the oscillation oscillator are performed by a piece which acts by direct physical contact on the tuning fork or on a piece integral with the tuning fork. For example, the present invention may constitute an improvement of the solutions proposed in patent documents EP 2 466 401 or US 3,208,287 , which disclose a resonator in which the oscillator and the escape wheel carry magnets, for example permanent magnets, so as to constitute a regulation and exhaust mechanism on the basis of magnetic interactions.

According to one embodiment, the movement of the invention comprises a mechanical pulse member which is connected and / or powered by a source of mechanical energy. Source mechanical energy can be the same as in a conventional mechanical watch, for example, the energy can come from a barrel spring that can be remounted manually or automatically, for example.

While the present invention allows the operation of a movement for a purely mechanical timepiece, the skilled person will be able to apply the technical solutions disclosed in the present description in the case of an electronic watch or in a mechanical watch using magnetic interactions.

Indeed, the present invention makes it possible, for the first time, to make a movement of an entirely mechanical timepiece with an oscillator of the tuning fork type. However, the proposed solution is applicable to any time base on the basis of a tuning fork resonator or oscillator.

The figure 1 shows the general shape of a watch tuning fork. The tuning fork 1 comprises the two blades or branches 3 and 4, connected by the base 5 so as to form the general shape of a U. The two blades 2 and 3 are preferably arranged in parallel in a single plane. The two blades 3 and 4 preferably have the same length. On the opposite side to the base 5, the ends of the blades 3 and 4 are free. They preferably each carry a mass 8, 9, respectively, which serves to reduce the frequency of oscillations of the tuning fork 1. The tuning fork comprises a rod 6 through which the base 5 is connected to a fastener 7. One end of the rod 6 is connected to the base 5 while the other end is connected to the attachment 7.

In the case of a watch, the attachment 7 is preferably secured to the movement of the watch. For example, the fastener 7 is connected, for example by screwing, to the plate or to a bridge. In the case where the timepiece is not a watch, or in the case where the oscillator of the invention is not associated with a timepiece, the attachment 7 can be attached to a support any.

To minimize the bulk, the rod 6 is preferably located above the base 5. It could also be below the base 5, as shown in FIGS. Figures 2A and 2B which does not change the behavior of the tuning fork.

The interest of the tuning fork is mainly due to the fact that its quality factor Q is much higher than that of a simple vibrating blade. Without wishing to be bound by the theory, the high quality factor Q of the tuning fork compared to that of a simple vibrating plate is related to the U-shaped configuration and the resulting oscillation modes. P. Ong, "Little known facts about the common tuning fork", Phys. Educ. 37 (2002), 540-542 .

In order to further increase the Q quality factor of the oscillator, the oscillator comprises or is preferably made of a material having low or very low internal friction. A sophisticated model of the explanation of the quality factor takes into account the viscous internal friction of the branches and the base of the tuning fork, as described by Andres Castellanos-Gomez, Nicolas Agrait, Gabino Rubio-Bollinger, "Forcegradient-induced mechanical dissipation of quartz tuning fork force sensors used in atomic force microscopy", Ultramicroscopy (2011) 111 (3), 186-190 .

Materials that meet the criterion of low internal friction are, for example, monocrystalline silicon or quartz. Of course, other materials having comparable internal friction and / or of the same order of magnitude can also be used. In general, other monocrystalline materials can be used in the manufacture of the oscillator 1 according to the invention.

It should be noted that oscillator 1 as a whole may comprise or be made of several materials. For example, the masses 8 and 9 are typically made of gold or other dense material, for example another heavy precious metal. The masses 8 and 9 reduce the frequency of the oscillator if desired, which may be the case in a mechanical timepiece. The present invention also covers the possibility that the masses 8 and 9 are zero or absent. On the other hand, the masses 8, 9 can be placed or oriented in another way than shown in FIG. figure 1 as disclosed, for example, in US Patent US 3,447,311 . The masses 8, 9 can be made in the form of layers deposited on the blades 3 and 4 and / or can be connected near or in the region of the ends and be oriented as shown in FIG. US 3,447,311 , for example.

On the other hand, the blades 3, 4 may be formed of several materials having low internal friction, as will be described later below. Then, the rod 6 and / or the fastener 7 preferably comprises a higher internal friction material, as will be described later.

However, it is preferable that the oscillator comprises a set 2 formed at least of the blades 3 and 4 and the base 5. This set 2 preferably comprises an entity formed of a single continuous material. This should not prevent the presence of other materials as described in this specification. According to the present invention, the oscillator 1 comprises a set 2 formed of a material A characterized by a low internal friction. For example, the material A is chosen from the weak internal friction materials described above, such as, for example, monocrystalline silicon or quartz, or monocrystalline materials in general. According to one embodiment, said oscillator 1, or at least said set 2, comprises or is formed of monocrystalline silicon and / or quartz.

According to one embodiment, the rod 6 comprises and / or is formed of the same material A. According to this embodiment, the rod 6 is part of the assembly 2. According to another embodiment, the rod 6 comprises and / or is formed of another material.

Since the assembly 2 comprises or is preferably formed of one or more low internal friction materials (materials A and optionally material A 'described later below), the quality factor Q of the oscillator is higher than in the case of a metal oscillator, for example. This increase in quality factor Q also applies to oscillation modes that may be designated as undesired in an oscillator serving as a timebase.

The figures 2 A and 2 B illustrate two oscillation modes of a tuning fork 1 following a pulse. The dotted and continuous lines show, respectively, the two positions of the peak-to-peak amplitude of the oscillator, that is to say the two positions which define the maximum deviation from the rest position where the blades 3 and 4 are parallel.

In the oscillation mode shown in Figure 2A , the blades 3 and 4 come closer and move away from each other during oscillations. The continuous line shows the moment and the position of the oscillation where the ends of the two blades are close together and the dotted line shows the position where the two blades are spaced relative to each other. This is the antisymmetric oscillation mode which is characterized by a very high quality factor is which represents the oscillation mode that one wishes to obtain in a tuning timebase.

On the other hand, in the oscillation mode shown in Figure 2B , the blades 3, 4 move in phase, that is to say oscillate parallel and simultaneously from one side to the other in the same plane. The oscillation illustrated in Figure 2B and that of the symmetrical oscillation mode.

The two oscillation modes, antisymmetric and symmetrical, respectively, are also illustrated in US Pat. US 3,208,287 , in which the non-desired symmetric mode ( figure 2 A) is considered "abnormal oscillation".

In both cases Figures 2A and 2B oscillations take place in the plane of the oscillator itself, that is to say in the plane corresponding to that on which the drawing of the figures 2 A and 2 B is shown. Other modes of oscillation that may exist do not have the same implication in the context of the present invention.

It should be added that the problems related to the symmetrical oscillation mode arise above all in the case where the oscillator is made of a low-friction material, such as quartz or monocrystalline silicon, for example. Indeed, the symmetrical oscillation mode ( Figure 2 B) is not observed in metal tuning forks, for example. In other words, the choice of the low-friction material, for example material A, makes the oscillator oscillable not only in the desired antisymmetric mode, but also in the undesired symmetrical mode.

In general, the symmetrical oscillation mode is favored by mechanical excitation because of a slightly lower quality factor, thus easier to "find". This last point applies in particular to the pulse on only one of the two blades, whether this pulse is mechanical or otherwise.

A difference between the two modes of antisymmetric and symmetrical oscillations illustrated in Figures 2A and 2B relates to the rod 6. As can be understood by comparing the dotted and continuous lines of the rod 6 to the Figure 2B , the symmetrical mode induces a transverse oscillation of the rod 6, which corresponds to the oscillation of a simple vibrating blade. This transverse oscillation generally takes place in the plane defined by the two blades 3, 4. On the other hand, in the case of antisymmetric oscillation ( figure 2 A) , the rod 6 performs longitudinal and / or axial oscillations, along the axis of the rod 6.

In the case of electric quartz watches, symmetrical oscillations ( Figure 2 B) are generally avoided by the simultaneous excitation of the two blades 3 and 4, exploiting the piezoelectric properties of quartz. The simultaneous pulse (at the same time) of the two blades 3, 4 is illustrated by the two arrows 10 in opposite directions in the figure 1 . Generally, in an electronic watch, electrodes are placed on or near the blades to be able to induce an antisymmetric oscillation. In general, electronic methods or algorithms are put in place to prevent symmetrical oscillation in electronic watches.

A simultaneous impulse of the two branches is also disclosed in the document US 3,208,287 . Finally, in the Accutron watch mentioned above, the pulse of the metal tuning fork also takes place on the two blades simultaneously.

An object of the present invention is to implement alternative solutions to prevent the symmetric oscillation mode of a tuning fork type oscillator, preferably in a resonator used as a time base.

In particular, it is an object of the present invention to implement an oscillator of the tuning fork type which can be induced in antisymmetric oscillations following an impulse on a single blade, therefore in the absence of a simultaneous pulse on the two blades.

An impulse on only one of the two blades of a tuning fork represents the preferred solution in the case of a mechanical resonator, that is to say time bases in which oscillations of the tuning fork are mechanically induced and maintained, without the use of electricity, electronics or piezoelectricity. According to a preferred embodiment of a mechanical movement and / or a mechanical timepiece of the invention, the oscillations are induced and maintained without the use of magnetism.

In a preferred embodiment, the movement of the invention and / or the timepiece of the invention comprises a mechanical pulse mechanism or mechanism capable of acting on one of the two blades of a tuning fork so as to induce it and maintain it in oscillation. Such an organ or mechanism is disclosed, for example, in the international application WO2013 / 045573, filed on September 27, 2012 on behalf of ASGALIUM UNITEC SA under the deposit number PCT / EP2012 / 069122 . The content of this patent application is explicitly incorporated by reference.

Requirement WO2013 / 045573 discloses a tuning fork mechanical resonator for mechanical clock movement with free escapement. A blade of this tuning fork carries at least one first pin associated with at least one first fork of an anchor, for pivoting said fork between first and second angular positions and alternately lock and release an escape wheel. The resonator comprises a conversion member integral with the ankle, arranged to, on the one hand, to transform the oscillations of the blade into rotational movements of the anchor by the transmission of pulses from the blade to the anchor, and on the other hand, transmitting mechanical energy from said anchor to the oscillator blade in the form of pulses. According to one embodiment of the mechanical pulse and / or regulation member, a support carrying pins is attached to the end of one of the two blades. The dowels cooperate with teeth defining an anchor fork. The anchor comprises a frame pivotally mounted on the movement and a pair of arms each of which carries a tooth to interact with the pegs on the support. The anchor then comprises a second pair of additional arms, each of which carries a pallet arranged to cooperate with an escape wheel. The resonator of the request WO2013 / 045573 operates in a similar way to conventional resonators because the oscillator carries two pins instead of a single pin and the special geometry of the anchor fork. Thus, the anchor is intended to pivot between a first position in which one of the vanes locks the escape wheel in rotation and a second position in which the other pallet locks the escape wheel. When the anchor pivots between one and the other position, the escape wheel is released to turn. The pivoting of the anchor is also used to give a pulse on one of the two pins of the support to ensure the maintenance of oscillations of the blade and thus the tuning fork as a whole. In another embodiment, the conversion member comprises a rocker and operates according to the principle of the lever arm. A free end of the rocker is pivotally mounted on the free end of a blade and the other end is engaged between the teeth of the fork of the anchor to cooperate with it and rotate the anchor.

Those skilled in the art will understand that the device disclosed in the application WO 2013/045573 serves both the timing energy distribution and time regulation based on the oscillations.

Requirement WO2013 / 045573 discloses a mechanical pulse member capable of acting on one of the two blades so as to induce and maintain said oscillation oscillator. A mechanical pulse member is preferably used in the timepiece according to the present invention.

According to a preferred embodiment, the quality factor Q ₂ of the symmetrical oscillation mode of the oscillator of the invention is reduced actively and in a targeted manner with respect to the quality factor Q ₁ of the antisymmetric oscillation mode. According to this embodiment, the present invention aims at reducing the quality factor of the symmetrical oscillations so as to favor oscillation in the desired antisymmetric mode. This implies, in fact, that each mode of oscillation has not only its own frequency, but also its own quality factor. In the context of this specification, Q ₂ represents the quality factor of the undesired symmetric oscillation mode, while Q ₁ represents the quality factor of the desired antisymmetric oscillation mode. In general, the quality factor is defined by the formula Q = 2π x (stored energy / energy lost in each period).

According to the preferred embodiments of the invention, the quality factor Q ₂ is reduced in a targeted manner by the construction of the tuning fork and in particular by the choice of materials used in the construction of the tuning fork. Preferably, the quality factor Q ₂ is reduced by the tuning fork geometry and / or the choice of the position of different materials having different characteristics.

According to a preferred embodiment, the oscillator of the invention comprises at least one second material which makes it possible to reduce the quality factor Q ₂ of the symmetrical oscillation mode. This second material is generally designated as material B in the present specification. The material B is preferably chosen from materials having a higher friction than the material A. Preferably, the material B is a material having a higher internal friction than that of quartz and / or monocrystalline silicon, by example. According to one embodiment, the material B is selected from metals, alloys, polycrystalline materials, amorphous materials, for example.

The internal friction of a material is associated with the ability of a solid material to convert its mechanical vibration energy into an internal energy. This inevitable degradation or loss of energy is manifested in several ways, for example by a transformation of the vibration energy into heat. The quality factor of an oscillator and the internal friction of the material depend on each other, as described in the publication of Clarence Zener, "Internal Friction in Solids," Proceedings of the Physical Society 52 (1940), pp. 152-166 , and also in the more recent publication of Hsi-Ping Liu and Louis Peselnick, "Internal Friction in Fused Quartz, Steel, Plexiglass, and Westerley Granite From 0.01 to 1.00 Hertz at 10-8 to 10-7 Strain Amplitude," Journal of Geophysical Research 88 (March 10, 1983) , pp. 2367-2379 . In these publications, the inverse of quality factor Q (i.e. 1 / Q) is used as a measure of internal friction.

In the context of the present invention, the inverse of the quality factor 1 / Q is preferably used to determine whether a given material is characterized by low or high internal friction. The quality factor Q of a material can be determined by those skilled in the art, as described in many publications from the past 50 years, see the references of the publication Ilan Vardi, "The quality factor in mechanical watchmaking", Bulletin of the Swiss Chronometry Society 75 (2014), pp. 53-61 .

According to a preferred method, the quality factor Q of a material can be determined on the basis of a single vibrating blade which is induced in free vibration.

In the present description, consistent with the articles cited above, the internal friction of a material A can be represented by 1 / Q _A , and the internal friction of a material B can be represented by 1 / Q _B .

According to one embodiment, a material A having a low internal friction is a material whose value 1 / Q (1 / Q _A ) is <0.02, preferably <0.01. According to a preferred embodiment, a material having a low internal friction is a material whose value 1 / Q (1 / Q _A ) is <0.001.

In terms of internal friction, the material A 'fulfills the same conditions as the material A. The values of 1 / Q for A' (1 / Q _{A '} ) are thus in the same ranges as the values 1 / Q for A (1 / Q _A ).

According to one embodiment, a material B having a high friction or greater than the material A is a material whose value 1 / Q (1 / Q _B ) is ≥ 0.02, preferably ≥ 0.05, for example ≥ 0.1 or more great.

According to a preferred embodiment, the materials A and A 'have an internal friction (1 / Q _A ) ≤0.01 and the material B an internal friction (1 / Q _B )> 0.02. Preferably 1 / Q _A <0.005 and 1 / Q _B ≥ 0.015.

In the context of the present invention, materials A and B are generally selected such that 1 / Q _A <1 / Q _B. Defining the materials A and B relative to one another ignores the particular conditions in which the respective Q quality factor (Q _A , Q _B ) has been measured to determine the value of the friction. internal material, provided that the conditions are the same for the determination of Q _A and Q _B (for example 25 ° C, and two rods, one of the material A and one of the material B, having identical dimensions).

According to a preferred embodiment, (1 / Q _A ) / (1 / Q _B ) (= Q _B / Q _A ) is ≤ 0.5, preferably ≤ 0.2. According to a preferred embodiment, Q _B / Q _A is ≤ 0.1, preferably ≤ 0.02, or even ≤ 0.01.

It should also be mentioned that the present invention contemplates the adjustment of the internal friction of a material (1 / Q _A and / or 1 / Q _B ) to obtain a material having the desired characteristics. For example, materials A and B may be mixtures, for example composites comprising a plurality of materials or materials, selected to provide a material having internal friction in accordance with the preferred values or proportions indicated above.

Surprisingly, the inventors have found that it is possible to prevent symmetrical oscillations by the geometrical configuration and / or the position of the material B in the tuning fork. Preferably, the material B is in contact with the material A of the oscillator.

According to one embodiment, the tuning fork of the invention comprises a material B which is arranged and / or located so as to prevent or dampen the symmetrical oscillations of the tuning fork.

According to one embodiment of the invention, the presence of the material B makes it possible to damp the transverse oscillations of the rod 6. Therefore, according to one embodiment of the invention, the material A is a first material and the said factor of quality Q ₂ is reduced by the presence of a second material B, this material B being in contact with said material A so that a transverse oscillation of said rod 6 is damped.

According to one embodiment, said quality factor Q ₂ of the symmetrical oscillation mode of said oscillator is reduced so that Q ₁ / Q ₂ is equal to or greater than 2. Preferably, Q ₁ / Q ₂ is equal to or greater than 5, equal to or greater than 10, equal to or greater than 20, equal to or greater than 50, or equal to or greater than 100, for example equal to or greater than 200.

According to one embodiment of the tuning fork according to the invention, the quality factor Q ₁ is at least an order of magnitude higher than the quality factor Q ₂ . By "order of magnitude" is meant a difference of about a factor of 10. Preferably, the quality factor Q ₁ is at least 1 to 3 orders of magnitude higher than the quality factor Q ₂ .

Those skilled in the art will appreciate that, in the context of the present invention, the quality factor Q is used both to describe the two modes of oscillation, antisymmetric and symmetrical, shown in FIGS. Figures 2A and 2B (Q ₁ and Q ₂ ), and as a parameter of the internal friction of a material. In the latter case, the inverse of the quality factor (1 / Q) is used. It should be mentioned that the state of the art describes several parameters which represent the internal friction of a material, such as the damping or loss factor tan δ, or the loss modulus G ". of the present invention, the inverse of quality factor Q is chosen, as proposed by C. Zener (1940) and H.-P. Liu et al (1983), especially because the measurement of this parameter and well known to the skilled person in the field of watchmaking.

The second material or material B can be arranged in the rod 6 of the tuning fork. According to one embodiment of the invention, said material A is a first material and the rod 6 comprises or consists of a second material B in contact with said first material.

According to one embodiment, the rod 6 is entirely made of the material B. Alternatively, the rod 6 comprises such a material B or several materials which, on the whole, fulfill the characteristic of the higher internal friction. It is considered advantageous if the material B is in contact with the material A. For example, the material B is in contact with the base 5 of the tuning fork. According to this embodiment, the material B is preferably at least at the interface of the material A with the rod 6.

This embodiment is illustrated by the figures 3 A to 3 C, wherein the rod 6 is made of a material B which is different from the material A, the assembly 2 is made. The assembly 2 comprises in particular the two blades 3,4 and the base 5.

Reference numbers of FIGS. 3A to 3C have the same meanings as described above for the figure 1 . The figure 3A shows the tuning fork in the rest position, while the Figures 3B and 3C show the antisymmetrical and symmetrical oscillations, respectively, following a given pulse on one of the two blades (here on the blade 3) at the level of the arrow 11.

In the embodiment illustrated in FIGS. 3A to 3C , the assembly 2 is constructed entirely of type A materials, thus with low internal friction, but the rod 6 is composed of a material having a greater internal friction (material B), for example, the metal used for the tuning fork classic watchmaker. In this embodiment, the antisymmetric oscillations of the Figure 2A have no loss by the stem, due to its zero transverse movement, while the symmetrical oscillations of the tuning fork ( Figure 2 B) are damped due to the energy lost at the attachment or the connection between the rod 6 and the base 5, and between the rod 7 and the attachment 7 of the tuning fork, due to the stresses S1 and S2, see the figure 3C . The quality factor (Q ₂ ) of the symmetric oscillations would therefore be comparable to the quality factor of a single vibrating blade embedded at one end made of this material B, so very small (for example <10).

The rod 6, made of material B having a higher internal friction than the material A of which the assembly 2 is manufactured, does not dampen or reduce the quality factor (Q ₁ ) of the antisymmetric oscillations illustrated in FIG. figure 3B . This also applies to the case where the tuning fork 1 is induced in oscillation by a pulse on a blade only, illustrated by the arrow 11.

It has been indicated in the US patent US 3,447,311 that the rod preferably has a certain flexibility or elasticity as a whole, which makes it possible to remove or move the frequency away from the symmetrical oscillations of the frequency of the antisymmetric oscillations. According to one embodiment, the rod 6 is arranged to retain sufficient flexibility and / or elasticity to separate the frequencies specific to the antisymmetrical and symmetrical mode. This arrangement can be achieved by the geometry and / or shape of the rod 6 and the material of which it is made. By varying the geometry of the rod, for example, by decreasing its width and / or increasing its length, one can increase its flexibility and thus retain the required elasticity. Preferably, the natural frequency of the symmetrical and antisymmetric oscillations are different and / or remote. By "natural frequency" is meant the concept of resonant frequency, where the amplitude is maximum with respect to the pulse frequency.

For example, the natural frequencies of symmetric and antisymmetric oscillations are at least 5 Hz, preferably at least 10 Hz, or even at least 20 Hz, and even at least 30 Hz.

According to one embodiment of the invention, the rod 6 is part of said assembly 2 comprising the blades 3, 4 and the base 5 and comprises or consists of said material A. According to this embodiment, illustrated in FIGS. Figures 4A to 4C , the rod 6, the base 5 and the blades 3, 4 may be manufactured in one piece, for example of a continuous material A, or may comprise a continuous material A. In the case of a monocrystalline material, the rod 6, the base 5 and the blades 3, 4 may comprise or be formed of a single crystal.

As shown in Figure 4A , the attachment 7 comprises or consists of a material having an internal friction higher than that of the material A. In this case, the rod 6 may or may not include a higher internal friction material (material B). As indicated, Figures 4A to 4C show in particular the possibility where the rod comprises and / or is made of the same material A as the base 5 and the blades 3, 4, and the attachment 7, illustrated by a dark square, is formed of the material B. Of course, the The present invention does not exclude the possibility that the rod comprises a material other than the material A of the base 5 and the blades 3, 4, this other material having a low internal friction, such as the material A, or a higher internal friction. , like material B.

According to one embodiment of the invention, said material A is a first material and said fixing member 7 comprises a second material B in contact with said rod 6.

In the embodiment shown in Figures 4A to 4C the damping of the symmetrical oscillations is introduced to the fastener 7, replacing the material A of the fastener 7 with a material which dissipates the oscillations of the rod 6. The rod 6 of material A is thus embedded in a base formed by the fastener 7 made of a material having a large internal friction, such as the watchmaking tuning fork metal, or another material such as a resin (material B).

One can also imagine that the rod 6 of material A is bonded to the attachment 7 by an adhesive that could serve as damping, so a loss of energy in the symmetrical mode, and a reduction of the quality factor of the symmetrical mode. The adhesive comprises and / or then constitutes the material B. In this case, the fastener 7 could also be made of a material chosen from the type A materials. The antisymmetric oscillations are not damped by the fastening, since there are no transverse oscillations of the rod 6 in the dissipative embedding 7, see the Figure 4B . On the other hand, the symmetrical oscillations are damped since the oscillations of the rod 6 are damped due to its fixation in the dissipative material 7, as indicated by the arrows D in the figure 4C . In this case, the stress S1 'between the rod and the base of the tuning fork does not dissipate more energy than in the case where the tuning fork and its attachment are entirely of material A. The constraint S1' does not therefore contribute to the reduction. symmetrical oscillations.

In one embodiment, said fastener 7 fixes and / or encases said rod 6 so that a transverse oscillation of said rod is damped. This embedding of the rod 6 is well illustrated at Figures 4A to 4C where the contact of the fastener 7 with the rod 6 causes the energy dissipation of the oscillations.

It should be added that the dissipation of energy coming from the damping of the symmetric oscillations as illustrated in FIGS. Figures 3C and 4C can lead to a heating, that is to say, the energy of the oscillations is transformed into heat. The loss of energy associated with an oscillation mode (here the symmetrical oscillation mode) explains the reduction of the quality factor of this type of oscillation. According to the present invention, the material B is positioned and / or arranged to cause particularly a loss of energy symmetrical oscillations to reduce the quality factor Q ₂ . Preferably, the material B is arranged so as to damp the transverse oscillations of the rod 6. As those skilled in the art will understand, the present invention seeks to exploit the difference between the antisymmetric oscillations of the Figure 2A and the symmetrical oscillations of the Figure 2B , as it is manifested at the level of the movement of the rod 6. It will also be noted that the center of gravity of the tuning fork is almost immobile in the antisymmetric case but makes a sensible movement in the symmetrical case.

According to one embodiment, said blades 3, 4 of the tuning fork 1 according to the invention comprise a material A ', said material A' being arranged as a layer on at least a part of the two blades. According to one embodiment, said material A 'is characterized by a weak internal friction similar to that of the material A. Preferably, the internal friction of the material A' is of the same order of magnitude as that of the material A.

According to one embodiment, the material A and the material A 'are distinguished with respect to the sign (positive or negative) of their respective coefficient of thermal expansion. Consequently, the coefficient of thermal expansion of said material A 'has a reverse sign with respect to the sign of the thermal coefficient of said material A. In other words, if the coefficient of thermal expansion of the material A is positive, for example +0.5, that of the material A 'is negative, for example -1.0.

An object of the choice of two materials, A and A 'with low internal friction is to cancel or at least partially compensate the effect of temperature on the frequency of oscillations. Generally, the frequency of oscillations decreases following a deviation of the optimal temperature (generally 25 ° C) of a tuning fork because of the increase or the decrease of the volume of the material whose tuning fork is made up. Since the material A 'preferably has a sign expansion coefficient opposite to that of the material A, the presence of A' reduces the change in the volume of the set A and A '.

The characteristic of the inverse sign does not imply that the absolute values of the thermal expansion coefficients of the materials A and A 'are identical (see the example of the values +0.5 and -1.0 given above). For this reason, the quantity of the material A 'is preferably chosen so that a change in volume of the assembly comprising at least the blades 3, 4 and the base 5, and possibly the rod 6 is reduced to the maximum, that is, the expansion or decrease in volume is essentially reduced or absent.

Preferably, the material A 'is also a low-friction material. Thus, the material A 'preferably does not have a significant effect on the quality factor Q ₁ . The person skilled in the art knows the materials with a coefficient of negative thermal expansion.

The material A 'is preferably present on at least the two blades 3, 4. The material A' may also be present on the base 5. If the rod 6 comprises or consists of the material A, ( Figures 4A to 4C ), the material A 'may also be present on the rod. It should be understood that the present invention is not limited to the way in which the material A 'is associated with the material A. For example, the material A' may be deposited as a layer on at least a portion of the material A or reverse. The person skilled in the art may consider other ways of associating the material A 'with the tuning fork according to the invention. Said layer may extend over an entire face of the blades 3, 4 and the base 5 and also on the rod 6, or may be present on only part of the assembly 2. Preferably, the material A 'is at least associated with and / or connected to a portion of the blades 3, 4. Preferably, the material A' is arranged equitably and / or symmetrically on the two blades 3, 4.

Those skilled in the art will not encounter any particular difficulty in adapting the content of the present disclosure to their own needs and implementing an oscillator different from that according to the embodiments described here, but in which the quality factor of the symmetrical oscillations is reduced with respect to the quality factor of the antisymmetric oscillations, without departing from the scope of the present invention. For example, a person skilled in the art will know how to use the oscillator according to the invention in a timepiece that is not entirely mechanical and / or in an electronic timepiece, or in an electronic timebase any. For example, the present invention can be easily implemented in an application that requires a time base, such as a computer or a mobile phone. In particular, the fact that the present invention makes it possible to excite and / or maintain the antisymmetric pulses despite the pulses (mechanical or otherwise) on only one of the two branches makes it possible to facilitate the construction of the tuning fork in general, also in the case of a tuning fork induces oscillation by electronic means and / or by using the piezoelectric effect in the case of the quartz tuning fork, for example.

Claims (16)

A timepiece comprising a mechanical watch movement comprising: a tuning fork oscillator (1), said oscillator comprising a set (2) comprising two blades (3, 4) and a base (5) connecting said blades, said oscillator ( 1) comprising a rod (6) connected to said base (5), the oscillator being connected by its rod (6) to a fixing member (7) connected to the movement, said assembly (2) comprising or consisting of a material A, said material A being characterized by a low internal friction, said movement comprising a mechanical pulse member capable of acting on one of the two blades so as to induce and maintain said oscillation oscillator, said oscillator being capable of oscillating in a desired antisymmetric mode as well as in an undesired symmetric mode, characterized in that the quality factor Q ₂ of the symmetrical oscillation mode of said oscillator is reduced with respect to the quality factor. Q ₁ of the antisymmetric oscillation mode. The timepiece according to claim 1, characterized in that said material A is a first material and in that said quality factor Q ₂ is reduced by the presence of a second material B, this material B being in contact with said material A so that a transverse oscillation of said rod (6) is damped. The timepiece according to claim 2, wherein said material B is characterized by an internal friction higher than that of said first material. The timepiece according to any one of claims 1 to 3, characterized in that said material A is a first material and in that the rod (6) comprises or consists of a second material B in contact with said first material. The timepiece according to any one of claims 1 to 4, characterized in that the rod (6) is part of said assembly (2) comprising the blades (3, 4) and the base (5) and comprises or is constituted by said material A. The timepiece according to any one of claims 1 to 5, characterized in that said material A is a first material and in that said fixing member (7) comprises a second material B in contact with said rod (6 ). The timepiece according to any one of claims 1 to 6, characterized in that said fixing member (7) fixes and / or encases said rod (6) so that a transverse oscillation of said rod is damped. The timepiece according to any one of claims 2 to 7, characterized in that said second material is selected from metals, alloys, polycrystalline materials, and / or amorphous materials. The timepiece according to any one of the preceding claims, characterized in that said oscillator (1), or at least said assembly (2), comprises or is formed of monocrystalline silicon and / or quartz. The timepiece according to any one of the preceding claims, characterized in that said blades (3, 4) comprise a material A ', said material A' being arranged in a layer on at least a portion of the two blades. The timepiece according to the preceding claim, wherein said material A 'is characterized by a weak internal friction similar to that of the material A. The timepiece according to claim 10 and / or 11, wherein the coefficient of thermal expansion of said material A 'has a sign (+/-) inverse with respect to the sign of the thermal coefficient of said material A. An oscillator of the tuning fork type (1), said oscillator comprising an assembly (2) comprising two blades (3, 4) and a base (5) connecting said blades, said oscillator (1) comprising a rod (6) linked to said base (5), the oscillator being connected by its rod (6) to a fixing member (7) connected to a support, said assembly (2) being formed of a material A, characterized by a weak internal friction, characterized in that said material a is a first material and in that said oscillator comprises a second material B, the material B being in contact with said material a such that a transverse oscillation of said rod (6) is damped. The oscillator according to claim 13, characterized in that said material B has an internal friction (1 / Q _B ) higher than the internal friction (1 / Q _A ) of the material A, so that Q _B / Q _A is ≤ 0.1. A watch movement comprising the oscillator of the preceding claim, said movement comprising a mechanical pulse member capable of acting on one of the two blades so as to induce and maintain said oscillation oscillator. The watch movement according to the preceding claim characterized in that said mechanical pulse member is connected and / or powered by a source of mechanical energy.

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